The Technical Electronic Product Radiation Safety Standards Advisory Committee met on May 17, 2001 in Rockville, MD. The following is a brief summary of the meeting. Transcripts of the actual meeting are located at http://www.fda.gov/ohrms/dockets/ac/cdrh01.htm
Ms. Lillian Gill, Acting Deputy Director for Science at CDRH, gave an update on some issues previously discussed by the Committee. First among these was the status of the proposed amendments to the federal performance standard for fluoroscopic x-ray systems (21 CFR 1020), which is anticipated to be published later this year.
Ms. Gill next discussed the proposed amendments to the U.S. laser standard (21 CFR Part 1040). The International Electrotechnical Commission (IEC) has unanimously approved and passed amendments to their standard. FDA is currently drafting amendments to Part 1040, and has prepared a guidance document which states that FDA will not object to laser products that do not comply with some FDA requirements if they compy with the comparable requirements of the IEC standards, such as classification.
The third issue addressed by Ms. Gill was FDA regulation of sunlamp products (21 CFR Part 1040). FDA met with members of the indoor tanning industry in September 2000 and discussed possible changes to the FDA performance standard in detail. More meetings and discussions are anticipated and, after a complete assessment of these discussions, FDA will propose specific amendments to the current performance standard to bring the regulations up to date.
Ms. Gill also updated the Committee on the status of a draft standard for personnel security screening systems utilizing x-ray radiation, or people scanners. The FDA does not currently have mandatory standards, but the N43 Committee of the American National Standards Institute has appointed a subcommittee of regulators, manufacturers, and users to draft a consensus standard. This subcommittee has held three meetings since the June 2000 TEPRSSC meeting, and is planning to submit their final draft to the main N43 committee for comment and balloting. The planned publication date is June 2002.
Following Ms Gill’s summary presentations, Dr Tom Shope, of the FDA introduced the discussion of digital x-ray modalities. Computed tomography (CT), has been in use for many years, and digital imaging systems for general radiology (DR), and computerized radiology (CR) are now becoming more common. Dr Shope indicated that there is little current, comprehensive national data on patient exposures, especially from DR and CR, and it would be useful to know more about actual patient dose as well as the long-term consistency of dose levels. FDA does conduct some studies in collaboration with state regulatory bodies. Data from the Nationwide Evaluation of X-ray Trends (NEXT) studies and other sources indicates that patient doses from CT are a significant portion of total medical exposures. State of the art continuous scan CT systems can scan larger patient volumes quickly and this has stimulated anew the clinical use of CT. The medical community is discussing the potential value of this modality for screening studies, and there is a concern that it may be utilized without justifiable indication. FDA is also concerned that the appropriate x-ray technique factors be used with children or small patients.
Dr Stanley Stern of FDA followed Dr Shope and discussed in more detail FDA activities and current thinking about recent developments in computed tomography. After reviewing data on pediatric CT dose, Dr. Stern solicited Committee input on whether the FDA should issue a formal notice about the potential for larger than needed dose and about appropriate CT technique for pediatric patients. On the issue of dose representation, Dr. Stern looked at how technology and practice have progressed beyond the applicability of dose indices and terminology defined 20 years ago with the adoption of the current U.S. mandatory standard for CT equipment performance. He described features and limitation of the computed tomography dose index (CTDI) in use, noting that it is defined only for axial scanning and that there is no U.S. standard for helical CT dosimetry. Dr. Stern stressed that the rapidity of change in CT practice and technology has left the field so unsettled that even the nomenclature is not standardized.
Dr. Stern stated that the FDA is currently thinking of a two step regulatory approach, with near term possible policy decisions on development of manufacturer guidance, and eventually amendments to the performance standards for CT equipment. These might include display of patient dose information, limitations on geometrically inefficient use of radiation, and adaptive x-ray tube current modulation (according to patient thickness), which offers the prospect of an automated way of obtaining an optimal radiation dose.
Dr. Robert Gagne of the FDA gave an overview of digital imaging technology and made some comparisons with conventional screen/film radiology. He described different types of digital radiography systems including flat panel imaging arrays, computed radiography systems, and CCD based-optically coupled systems. He noted that while the installed base of DR systems is still small, the medical community is receptive to continued adoption of these devices since patient data can be more easily stored and transmitted. Patient dose is a concern because screen/ film radiography inherently places more limits on patient dose, since the exposure range for producing an acceptable film is more narrow. Digital systems can deliver a readable image over a wider range of exposure levels even if this results in overexposing patients. There is also the possibility that exposure levels may be raised to compensate for equipment problems. Dr. Gagne urged that facilities using DR institute quality assurance programs, and monitor patient exposure levels. He also suggested that FDA may consider the possibility of changing the diagnostic x-ray Performance Standard to require a dose display at the operator’s console for all radiographic equipment. This would make it much easier to track patient exposure and establish reference dose levels.
The Committee encouraged FDA to consider requiring a meaningful dose indicator on CT scanners that is consistent with other national and international bodies. The Com-mittee also urged FDA to investigate the best mechanism for DR and CR systems to provide a patient dose indication and to define with reference to national and inter-national standards what the most appropriate indicator is. FDA was advised to consider whether all conventional radiographic systems should provide a post exposure display of the product of tube current and exposure time. FDA was encouraged to investigate the development of educational programs and materials for physicians and technicians regarding the meaning and use of this information.
Mr. Collin Figueroa of FDA discussed FDA oversight of non-medical radiation producing products, and relevant performance standards. He gave some examples of non-medical products that have performance standards such as television sets (TV), microwave ovens, and lasers. The agency reviews radiation safety product reports and carries on post-market surveillance activities. Whenever acceptable, FDA supports the development of consensus standards, and attempts to harmonize with recognized national and international standards.
TV receivers and monitors can include video display products containing a component capable of generating x-rays. Mr Figueroa reviewed the radiation standard for TV receivers and monitors and described changes in the technology and use of these items. FDA information indicates that some manufacturers lack understanding of the appropriate testing requirements and processes. Mr. Figueroa reviewed the radiation standard for microwave ovens and the changes in technology over the years. FDA is concerned in some instances about the design of doors and interlocks, and manufacturers methods of leakage testing. Mr. Figueroa also discussed the radiation standard for laser products and the amendments in the process of moving forward. He noted the increase in the number of laser products over the years, not only in commercial applications, but as toy and novelty devices. Many products are imported from overseas.
Dr. Russell Owen of FDA, the final presenter, discussed the possible biological effects of radiation emitted from cellular telephones. There is a public concern over a possible link to cancer because of the unprecedented and chronic exposure of a handheld electronic device that is near the body for a long time. There are few epidemiological studies, particularly of highly exposed populations, and the difficulties in exposure assessment such as actual phone position and use remain to be resolved. Dr Owen stated that longer follow-up than the three years currently available is needed for study of association with long latency diseases and cumulative effects.
Human studies of R/F exposure have so far found no association with increased brain or nervous system cancers or leukemia. Animal studies have provided mixed results, with some short term ones showing positive tumor associations which have not been replicated. Dr. Owen stressed the need for ongoing research in engineering, science, and cellular biology, where guidelines and standards for testing methodology can be further refined. FDA is currently conducting animal studies, and trying to develop models for exposure assessment. As part of a cooperative research program agreement with the Cellular Telephone Industry Association, FDA provides scientific and technical oversight on research contracts. There are also ongoing collaborations between FDA, the National Institute for Occupational Safety and Health, the National Institutes of Health, the FCC, and the EPA, as well as the International Commission on Non-Ionizing Radiation Protection.